1. Field of the Invention
The present invention relates to managing memory in displaying data storage system information.
2. Description of Prior Art
Information services and data processing industries in general have rapidly expanded as a result of the need for computer systems to manage and store large amounts of data. As an example, financial service companies such as banks, mutual fund companies and the like now, more than ever before, require access to many hundreds of gigabytes or even terabytes of data and files stored in high capacity data storage systems. Other types of service companies have similar needs for data storage.
Data storage system developers have responded to the increased need for storage by integrating high capacity data storage systems, data communications devices (e.g., switches), and computer systems (e.g., host computers or servers) into so-called “storage networks” or “Storage Area Networks” (SANs.)
In general, a storage area network is a collection of data storage systems that are networked together via a switching fabric to a number of host computer systems operating as servers. The host computers access data stored in the data storage systems (of a respective storage area network) on behalf of client computers that request data from the data storage systems. For example, according to conventional applications, upon receiving a storage access request, a respective host computer in the storage area network accesses a large repository of storage through the switching fabric of the storage area network on behalf of the requesting client. Thus, via the host computer (e.g., server), a client has access to the shared storage system through the host computer. In many applications, storage area networks support hi-speed acquisitions of data so that the host servers are able to promptly retrieve and store data from the data storage system.
Conventional storage area network management applications typically include a graphical user interface (GUI) that enables a network manager to graphically manage, control, and configure various types of hardware and software resources associated with a corresponding managed storage area network. For example, one conventional storage management application generates a graphical user interface utilized by a storage administrator to graphically select, interact with, and manage local or remote devices and software processes associated with the storage area network. Based on use of the graphical user interface in combination with an input device such as a hand operated mouse and corresponding pointer displayed on a viewing screen or other display, a storage administrator is able to manage hardware and software entities such as file systems, databases, storage devices, volumes, peripherals, network data communications devices, etc., associated with the storage area network. Consequently, a storage management station and associated management software enables a storage administrator (a person responsible for managing the storage network) to manage the storage area network and its resources.
One example of this kind of graphical user interface includes a screen presentation that may include toolbars with accompanying menus and menu items as well as displays such as graphs, maps or trees.
In a display to which the term “tree” presentation or display is applied, one element in the tree is visually connected from another element in the tree somewhat reminiscent of a tree-branching, giving rise to the term. This display would be familiar to users of various commercially-available software packages, such as Microsoft's Windows Explorer® software. The element at treetop is normally called a “root node” or “parent” and elements connected directly below and from that root node are termed “children” of that root node. Children of that root node's children are “grandchildren” of the root node, etc., comprising the “descendents” of that root node. Any child node in the descendent hierarchy can be selected or considered as a “local root node” for its descendents. These displayed nodes, which are visible to computer users, are normally constructed within the computer system or network as software “objects” which are then handled or controlled by object-oriented software running in the system or network.
A typical computer network being used today that can run object oriented software is a client-server network, the client being the user (GUI) or workstation and the server being software (discrete or distributed throughout the network) which serves the client. In this network, a computer system can employ one or more object-oriented computer languages such as C++, XML (eXtensible Markup Language), Java, and/or others. Briefly, an object, in computer software terms, is a dedicated area of memory which can be thought of as an impervious container holding both data and instructions within itself, both defining itself and its relationships to other objects in the computer system or network. Such object or node can send and receive messages to and from other objects, respond and react to such messages (e.g. commands) but shall normally be impervious to internal scrutiny. For example, in a computer data storage system (a kind of computer) each object (system object) may describe or relate to a specific tangible detail in the storage system or in the storage system's processor (e.g., details such as those describing or relating to aspects of operation of the processor's cooling-fan, power switch, cache memory, power supply, disk drive interface, individual disks, etc.). These tangible objects (nodes) within the storage processor in the storage system can send messages to each other within the storage system and to other objects outside the storage system over the network with which they are operatively coupled. The relationship between these specific objects in the storage processor is usually visualized or characterized as the tree to which reference was earlier made. In this tree, many children may typically hang from the same parent. In addition to these kinds of tangible objects, logical units (LUNs) are other nodes or objects that can be contained within a tree. Also, the storage processor itself and/or the storage system itself can be objects and interact as individual nodes, respectively, with other nodes in their network.
The tree relationship of these node objects may be displayed in tree fashion on the terminal screen of the GUI. This display is controlled, in part, by a large, fixed body of complex code which “paints” this tree display on the terminal screen.
With respect to the complex code, people today use the World Wide Web for a variety of different and diverse tasks for example locating information, ordering and buying goods on-line and managing their finances. Many users expect that these applications will operate regardless of what type of computer platform is used.
Java technology, which is a trademark of Sun Microsystems, Inc, helps provide a solution by allowing the creation of computer platform independent programs. The Java technology includes an object orientated programming language and a platform on which to run the Java applications. Java is both a compiled and an interpreted language. The source code that has been written by the application developer is compiled into an intermediate form called a Java bytecode, which is a platform independent language. At a client machine, the java bytecodes are interpreted by the Java platform and the Java interpreter parses and runs each Java bytecode instruction on the computer. (If the Java bytecode is run as a applet, it may first be sent over the network to the client machine.)
Java's objected orientated programming language is based on using objects and classes and this paragraph will introduce the reader to a few basic concepts. Just like real world objects, software objects consist of a state and a behavior. A software object maintains its state in one or more variables and a variable is an item of data named by an identifier. A software object implements its behavior with methods and a method is a function associated with an object. Just like any other objected orientated programming language objects communicate with each other by passing messages. Further object orientated concepts are well known in the art and will not be described here further.
The Java platform includes the Application Programming Interface (API), which is a large collection of ready-made software components, which provide a variety of capabilities, and the Java Virtual Machine (JVM) which will be explained in the paragraph below. Together the JVM and the API sit on top of the hardware based computer platform and provide a layer of abstraction between the Java program and the underlying hardware.
The JVM is made up of software, which can run a Java program on a specific computer platform of a client machine. Before a Java program can be run on a JVM, the Java program must first be translated into a format that the JVM recognizes, which is called a Java class file format. The Java class file format contains all the information needed by a Java runtime system to define a single Java class.
The JVM running on a particular computer can be divided into four basic parts: the registers, the stack, the garbage-collected heap, and the method area.
Like at least some other object-orientated applications, a Java application typically allocates new objects to a region of the system memory within a data processing system commonly referred to as the ‘heap’ and each JVM has its own heap. Java does not have a ‘free’ or ‘delete’ method, which allows a Java application to free objects that are no longer required by the system. Instead when a Java application executes on a particular computer platform the Java application relies on a garbage collection process which is the responsibility of the JVM, to reclaim space within the heap that is no longer utilized by previously allocated objects.
In general, an object is determined as being live while there is an object reference pointer to it somewhere in the active state of the JVM and therefore the object is able to be located. When an object ceases to be referenced from the active state within the JVM it can be classified as garbage. The memory space occupied by the object can then be reclaimed for reuse and garbage collected. Garbage collection is usually triggered whenever the Java application attempts to create a new object, and it is determined that there is insufficient free space available within the heap to satisfy an object allocation.
Garbage collection is usually performed in a synchronous manner. Generally, the synchronous garbage collection begins its operation by temporarily stopping all Java applications within the JVM. The synchronous garbage collection then traverses a Java stack and the heap in order to search for all the active objects and their children. These active objects and their children are then marked accordingly. Afterwards the heap is searched again for a second time to reclaim any space previously utilized by the unmarked objects. Finally the Java applications are restarted again. This type of garbage collection is typically called “stop the world” as all applications are stopped while garbage collection is performed and restarted when the garbage collection process has finished.
One way to overcome part of the performance penalty of automatic garbage collection is to create groups of objects known as object pools that are still in use as far as the garbage collection mechanism is concerned, but are actually not used. When a new object is needed, one of these objects in the pool can be returned without going to the heap to allocate a new storage element. Pools thus provide one way to “recycle” used objects in a way that provides significant performance benefits.
A technique for finer grain of control for Java program's interaction with the garbage collection is Reference Object Application Programming Interface (API). The reference object encapsulates a regular reference to a Java object. The API defines the following reference types: soft reference, weak reference, and phantom reference in order of reachability. The impact on garbage collection is that the weaker the reference the more the incentive for the garbage collector to free its memory. Creating appropriate references using the Reference Object API gives the programmer more control over what memory is freed by the garbage collector.